Electronic device including a tunnel structure

ABSTRACT

An electronic device can include a tunnel structure that includes a first electrode, a second electrode, and tunnel dielectric layer disposed between the electrodes. In a particular embodiment, the tunnel structure may or may not include an intermediate doped region that is at the primary surface, abuts a lightly doped region, and has a second conductivity type opposite from and a dopant concentration greater than the lightly doped region. In another embodiment, the electrodes have opposite conductivity types. In a further embodiment, an electrode can be formed from a portion of a substrate or well region, and the other electrode can be formed over such portion of the substrate or well region.

FIELD OF THE DISCLOSURE

The present disclosure relates to electronic devices and processes offorming electronic devices, and more particularly to, electronic devicesincluding a tunnel structure and processes of forming the same.

RELATED ART

Integrated circuits can include a logic block that includes a dataprocessing unit, such as a central processing unit, a graphicalprocessing unit or the like, and a memory block that stores data thatcan be used by the data processing unit or stored within a hard drive,storage network, or other large memory device. The memory block caninclude volatile memory, nonvolatile memory, or a combination thereof.Many nonvolatile memories include additional layers as compared totransistors within the logic block. A conventional nonvolatile memorycan include a charge storage layer disposed over a substrate, and acontrol gate overlying the charge storage layer. The charge storagelayer can include a floating gate layer, a nitride layer, a layer ofnanocrystals or nanoclusters, or the like. The additional layersincrease costs, increase production times, and reduce yield.

Some integrated circuits have memory cells with only one gate electrodelayer. Such integrated circuits can use a single gate layer to form thegate electrodes for nonvolatile memory cells and transistors within thelogic block. A combination of separate charge storage and control gatelayers is not needed. The process to make such integrated circuits isreferred to as a single poly process, as the nonvolatile memory cellscan be made with only a single layer of polycrystalline silicon.

FIG. 1 includes a schematic diagram of a portion of a conventionalnonvolatile memory array 10 that can be made with a single poly process.The nonvolatile memory array 10 includes four memory cells 100, 101,110, and 111 that are arranged in rows and columns. Each memory cellincludes capacitors 12 and 14, a state transistor 16, and an accesstransistor 18. Electrodes of the capacitors 12 and 14 and the gate ofthe state transistor 16 are connected to one another at an electricallyfloating node. The capacitors 12 and 14 are in the form of p-channelmetal-insulator-semiconductor field-effect transistor structures. Suchstructures are hereinafter referred to as “PMOS capacitors.” The stateand access transistors 16 and 18 are n-channel transistors and areconnected in series within each nonvolatile memory cell.

Other electrodes of the capacitors 12 are electrically connected tocontrol lines 140 and 141, and other electrodes of the capacitors 14 areelectrically connected to erase lines 130 and 131. Sources of the statetransistors 16 are electrically connected to a common ground, and thedrains of the access transistors 18 are electrically connected to bitlines 170 and 171. The gates of the access transistors 18 areelectrically connected to access lines 150 and 151. The memory arrayfurther includes p-channel transistors 1900 and 1901. Drains of thep-channel transistors 1900 and 1901 are electrically connected to thedrains of the access transistors 18 within the memory cells 100 and 101,respectively, sources of the p-channel transistors 1900 and 1901 areelectrically connected to a V_(DD) line 180, and gates of the p-channeltransistors 1900 and 1901 are electrically connected to a read-enableline.

FIG. 2 includes a table with voltages used to read, erase, and programthe memory cells 100, 101, 110, and 111. In FIG. 2, BL refers to bitlines, AL refers to access lines, CL refers to control lines, EL refersto erase lines, and RD_en refers to the read enable line. As will bediscussed in more detail later in this specification, the architectureof the nonvolatile memory cell and its use can result in erase disturband reliability issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes a schematic diagram of a portion of a conventionalnonvolatile memory array. (Prior Art)

FIG. 2 includes an operating table with voltages used to read, erase,and program the memory cells in the nonvolatile memory array of FIG. 1.(Prior Art)

FIG. 3 includes a depiction of an integrated circuit that includes anonvolatile memory cell array, a program unit, an erase unit, and a readunit in accordance with an embodiment.

FIG. 4 includes a schematic diagram of a portion of a nonvolatile memoryarray in accordance with an embodiment.

FIG. 5 includes an operating table with voltages used to read, erase,and program the memory cells in the nonvolatile memory array of FIG. 4.

FIG. 6 includes an illustration of a cross-sectional view of a portionof a workpiece including a substrate after forming an insulating layerand field isolation regions.

FIG. 7 includes an illustration of a cross-sectional view of theworkpiece of FIG. 6 after forming well regions.

FIGS. 8 and 9 include illustrations of a top view and a cross-sectionalview, respectively, of the workpiece of FIG. 7 after forming adielectric layer and a patterned conductive layer.

FIG. 10 includes an illustration of a cross-sectional view of theworkpiece of FIGS. 8 and 9 after forming doped regions within the activeregions not covered by the patterned conductive layer and after forminginsulating spacers.

FIG. 11 includes an illustration of a cross-sectional view of theworkpiece of FIG. 10 after forming heavily doped regions within portionsof the active regions.

FIG. 12 includes an illustration of a cross-sectional view of theworkpiece of FIG. 11 after forming a substantially completed nonvolatilememory cell.

FIGS. 13 to 16 include illustrations of cross-sectional views of tunnelstructures in accordance with other embodiments.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings. However, other teachings can certainlybe utilized in this application. While numerical ranges are describedherein to provide a better understanding of particular embodiments,after reading this specification, skilled artisans will appreciate thatvalues outside the numerical ranges may be used without departing fromthe scope of the present invention.

The term “coupled” is intended to mean a connection, linking, orassociation of two or more electronic components, circuits, systems, orany combination of: (1) at least one electronic component, (2) at leastone circuit, or (3) at least one system in such a way that a signal(e.g., current, voltage, or optical signal) may be partially orcompletely transferred from one to another. A non-limiting example of“coupled” can include a direct electrical connection between electroniccomponent(s), circuit(s) or electronic component(s) or circuit(s) withswitch(es) (e.g., transistor(s)) connected between them. Thus, anelectrical connection is a specific type of coupling; however, not allcouplings are electrical connections.

The term “heavily doped” is intended to mean a dopant concentration thatis at least 1×10¹⁹ atoms/cm³.

The term “intermediate doped” is intended to mean a dopant concentrationthat is (1) between 1×10¹⁷ atoms/cm³ and 1×10¹⁹ atoms/cm³ or (2) higherthan an adjacent lightly doped region and lower than an adjacent heavilydoped region. Thus, an intermediate doped region can have a dopantconcentration of 1×10¹⁶ atoms/cm³ when near a lightly doped regionhaving a dopant concentration of 1×10¹⁵ atoms/cm³ and near a heavilydoped region.

The term “lightly doped,” except when referring to a lightly-doped drain(“LDD”) region, is intended to mean a dopant concentration that is nogreater than approximately 1×10¹⁷ atoms/cm³.

The term “LDD region” is intended to mean a doped region near a sourceregion, a drain region, or a source/drain region of a transistor,wherein such doped region can help to reduce hot carrier degradation ofthe transistor. In many embodiments, an LDD region can have a dopantconcentration that is in a range of approximately 1×10¹⁶ atoms/cm³ toapproximately 1×10¹⁸ atoms/cm³. LDD regions may also be called extensionregions.

The term “metal” or any of its variants when referring to a material isintended to mean to a material that includes an element that is withinany of the Groups 1 to 12, within Groups 13 to 16, an element that isalong and below a line defined by atomic numbers 13 (Al), 31 (Ga), 50(Sn), 51 (Sb), and 84 (Po). Metal does not include Si or Ge.

The terms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a method, article, or apparatusthat comprises a list of features is not necessarily limited only tothose features but may include other features not expressly listed orinherent to such method, article, or apparatus. Further, unlessexpressly stated to the contrary, “or” refers to an inclusive-or and notto an exclusive-or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or notpresent), A is false (or not present) and B is true (or present), andboth A and B are true (or present).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read such that the plurals include one or at least one and thesingular also includes the plural, unless it is clear that it is meantotherwise. For example, when a single item is described herein, morethan one item may be used in place of a single item. Similarly, wheremore than one item is described herein, a single item may be substitutedfor that more than one item.

Group numbers corresponding to columns within the Periodic Table of theelements use the “New Notation” convention as seen in the CRC Handbookof Chemistry and Physics, 81^(st) Edition (2000-2001).

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the semiconductor and electronic arts.

A novel memory architecture for a nonvolatile memory array, physicaldesign, and methods of using the memory array can be used to improveresistance to erase disturb and improve reliability of the nonvolatilememory array. In particular, the orientation of the erase lines andprogramming and erasing methods can allow charge carriers to tunnelwithin different components within a memory cell. Charge carriers may betransferred through dielectric layers of different component, as opposedto a single dielectric layer within a single component. Thus,reliability is improved as the memory cells can withstand moreprogram-erase cycles at a particular failure level as compare to thememory array as described with respect to FIG. 1. Further, lowerprogramming and erase voltages may be used and still allow an acceptablethreshold voltage (“V_(T)”) window between programmed and erased memorycells to be achieved. More details regarding the memory architecture,physical design, and methods of using the memory array are described inmore detail in reference to the figures that follow.

FIG. 3 includes a logic depiction of an integrated circuit 20 thatincludes a nonvolatile memory (“NVM”) cell array 22 that is coupled to aprogram unit 24, an erase unit 26, and a read unit 28. Each of theprogram, erase, and read units 24, 26, and 28 can be used to provideappropriate voltages to the NVM cell array 22 for programming, erasing,and reading of memory cells within the NVM cell array 22. The units 24,26, and 28 can include transistors, capacitors, resistors, diodes, andthe like that can be connected to form a logic gate, a voltage divider,a charge pump, a switch, a latch, a column or array strobe, a senseamplifier, another circuit commonly used with nonvolatile memory arrays,or any combination thereof. Although the units 24, 26, and 28 aredepicted as separate units, operations can be combined. For example, asingle charge pump may be used for programming and erasing, or the samevoltage divider may be used for programming and reading. Thus, FIG. 3 ispresented to provide a basic understanding of different parts of theintegrated circuit 20 at a conceptual level and not to constrain thearchitecture, physical design, or operation of the NVM array.

FIG. 4 includes a schematic diagram of a portion of an NVM array 31. Ina particular embodiment, the NVM array may be used in the integratedcircuit 20 of FIG. 3. The NVM array 31 includes four memory cells 3100,3101, 3110, and 3111 that are arranged in rows and columns. In aparticular embodiment, the memory cells 3100, 3101, 3110, and 3111 arewithin the same sector and along immediately adjacent rows and columns.In the embodiment as illustrated in FIG. 3, each row of the NVM array 31is driven by three terminals coupled to three lines: an access line, acontrol line, and an erase line. Each column of the NVM array is drivenby two terminals coupled to two lines: a bit line and an access line.One terminal drives the whole array: the bulk.

Each memory cell includes a capacitor 32, a tunnel structure 34, a statetransistor 36, and an access transistor 38. Each of the capacitor 32 andtunnel structure 34 includes electrodes with a dielectric disposedbetween the electrodes. In an embodiment, the capacitor 32, the tunnelstructure 34, or both can be formed from transistor structures. In thisembodiment, each of capacitor 32 and tunnel structure 34 have anelectrode referred to as a gate, and another electrode referred to asthe active. In a particular embodiment, the capacitor 32 is a PMOScapacitor. The tunnel structure 34 can include many different physicaldesigns that are described in more detail later in this specification.In another embodiment (not illustrated), the capacitor 32, the tunnelstructure 34, or both may be implemented as thin-film capacitors.

Each of the state and access transistors 36 and 38 includes a sourceregion, a drain region, a body region, a gate dielectric layer, and agate electrode. In an embodiment, the state and access transistors 36and 38 are n-channel transistors. The gates of the capacitor 32, thetunnel structure 34, and the state transistor 36 are connected to oneanother at an electrically floating node called the floating gateelectrode. The drain region of the state transistor 36 and the sourceregion of the access transistor 38 are coupled to each other, and in aparticular embodiment, the state and access transistors are electricallyconnected in series. For each of the memory cells 3100, 3101, 3110, and3111, the drain of the access transistor 38 is the drain of the memorycell. The source of the state transistor 36 is the source of the memorycell. The gate of the access transistor 38 is the access gate of theaccess-gate memory cell. The active electrode of the capacitor 32 actsas the control gate of the memory cell. The active electrode of theerase structure 34 acts as the erase gate of the memory cell.

Each bit line is coupled to the drains of memory cells along at leastpart of the corresponding column. Each source line is coupled to thesources of memory cells along at least part of the corresponding column.Each access line is coupled to the access gate of memory cells along atleast part of the corresponding row. Each control line is coupled to thecontrol gate of memory cells along at least part of the correspondingrow. Each erase line is coupled to the erase gate of all memory cellsalong at least part of the corresponding row. Referring to the NVM array31, cells 3100 and 3101 have their access, control, and erase gatescoupled to the access line 3150, control line 3140 and erase line 3130,respectively. Cells 3110 and 3111 have their access, control, and erasegates coupled to the access line 3151, control line 3141 and erase line3131, respectively. Cells 3100 and 3110 have their drains and sourcesconnected to bit line 3170 and source line 3160, respectively. Cells3101 and 3111 have their drains and sources connected to bit line 3171and source line 3161, respectively. The bulk (e.g., the substrate or awell region within the substrate for the state and access transistors)of all cells are grounded. In the embodiment as illustrated in FIG. 4,each of the couplings as mentioned in this paragraph can be in the formof electrical connections. For example, the source regions of the statetransistors 36 are electrically connected to source lines 3170 and 3171,and the bodies of the state and access transistors 36 and 38 areelectrically connected to ground or V_(SS).

FIG. 5 includes a table with voltages used to read, erase, and programthe NVM array 31, including memory cells 3100, 3101, 3110, and 3111. InFIG. 5, BL refers to bit lines, AL refers to access lines, CL refers tocontrol lines, EL refers to erase lines, and SL refers to the sourcelines. In FIG. 5, during a read operation, V_(Dread) is the voltageapplied to the drain of the memory cell that is being read. V_(Access)can be approximately at V_(DD) for the integrated circuit. In aparticular embodiment, V_(DD) can be in a range of approximately 0.9 to5 volts. V_(Gread) can be selected so that current can flow out of anunprogrammed or erased memory cell. In a particular embodiment,V_(Gread) can be in a range of approximately 0 volt to approximatelyV_(DD). With respect to erase and program pulses, V_(PP) can be in arange of approximately 8 to approximately 25 volts. V_(inhibit) can bein a range of approximately 1.8 volts to approximately ½ V_(PP).

After reading the specification, skilled artisans will appreciate thatthe particular voltages used can vary depending on the technology andphysical parameters (for example, thickness of a tunnel dielectriclayer) of the memory cells. Further, although absolute values ofvoltages have been given, the voltage differences between the terminalsare more significant than the absolute values of the voltages on theterminations. For example, during an erase pulse, the voltage differencebetween the selected erase line and the other lines is approximatelyV_(PP). In another embodiment, the selected erase line may be at +¾V_(PP) and the other lines can be at approximately −¼ V_(PP). Such anembodiment may be useful if a breakdown voltage (for example, if anenable transistor within the erase unit has a drain-to-sourcepunchthrough voltage less than V_(PP)) or another concern is present.The read or program operation may be performed in addition to or insteadof the erase operation.

The memory architecture and operation of the NVM array 31 allows forbetter reliability and less problems with disturbing data in unselectedmemory cells during an erase operation. When comparing the schematicdiagrams of FIGS. 1 and 4, the orientation of the erase lines aredifferent. In FIG. 4, the erase lines 3130 and 3131 are oriented in thesame direction as the control lines 3140 and 3141. In a particularembodiment, the erase and control lines 3130, 3131, 3140, and 3141 areoriented along rows of memory cells. Compare this to the memory array 10in FIG. 1 that has an orthogonal relationship between the erase linesand control lines. More particularly, in which the erase lines 130 and131 are oriented along columns of memory cells, and the control lines140 and 141 are oriented along columns of memory cells.

Referring to the NVM array 31, during a program pulse for a selectedmemory cell, electrons tunnel from the channel of the state transistor36 to the floating gate electrode through the gate dielectric layer ofthe state transistor 36. During an erase pulse, electrons tunnel fromthe floating gate electrode to the active electrode of the tunnelstructure 34, via a tunnel dielectric layer of the tunnel structure 34.Thus, electrons tunnel through the gate dielectric layer of the statetransistor 36 during programming, and electrons tunnel through thetunnel dielectric layer of the tunnel structure 34 during erasing.Referring to the memory array 10 in FIG. 1, electrons tunnel through thedielectric layer of the capacitor 14 during programming and erasing. Asmore charge carriers, such as electrons, pass through the samedielectric layer of the same component, more defects are generatedwithin the dielectric. If the accumulated defects within the dielectriclayer become too large, the dielectric layer breaks down and renders thememory cell inoperable. Thus, a memory cell within the NVM array 31 mayhave better reliability because charge carriers tunnel through differentdielectric layers of different components during programming anderasing, as compared to a memory cell within memory array 10 wherecharge carriers tunnel through the same dielectric layer of the samecomponent during programming and erasing.

Erase disturb can be reduced or even substantially eliminated with theNVM array 31. During an erase pulse, memory cells are erased as a row oras a segment of a row, such as a word. The selected erase line is at aparticular voltage, such as V_(PP), and all other lines are atsubstantially the same voltage, such as 0 volts, which is different fromthe particular voltage. Thus, other than the floating gate electrode,all electrodes of unselected cells are at about the same voltage, whichsignificantly reduces the likelihood of an unselected memory cell beingdisturbed during an erase pulse. Referring to the memory array 10,memory cells are to be erased on a bit-by-bit basis. Thus, during anerase pulse, different voltages are used on the electrodes of unselectedmemory cells. The source regions of the state transistors 16 are atground, the erase line 130 is at 10 volts, the erase line 131 is atV_(DD), the control line 140 is at 0 volts, and the other control line141 is at 0 volts. Thus, during an erase pulse, any of the unselectedmemory cells within the memory array 10 will have a voltage differencebetween at least two of (i) a source region of the state transistor 16,(ii) an electrode of the capacitor 12, and (iii) an electrode of thecapacitor 14. The likelihood of erase disturb increases with the productof the voltage difference and time. If memory cell 100 in the memoryarray 10 is frequently programmed and erased, the other memory cells101, 110, and 111 have a greater likelihood of an erase disturb problem,particularly if memory cells 101, 110, and 111 are programmed and erasedinfrequently. Thus, the likelihood of an erase disturb issue issignificantly less with the NVM array 31 when using voltages in thetable of FIG. 5 than with the memory array 10 in FIG. 1 when usingvoltages in the table of FIG. 2.

A variety of physical designs can be used with the NVM array 31. Thelayout of memory cell as illustrated is merely to simplify understandingof the different parts of the memory cell. Skilled artisans willappreciate that other layouts can be used to achieve a more compactmemory cell. The description below provides some embodiments that can beused. For example, the NVM array 31 can be formed using a single polytype of process. Separate floating gate and control layers are notrequired. After reading this specification, skilled artisans willappreciate that many other embodiments can be used without deviatingfrom the scope of the appended claims.

FIG. 6 includes an illustration of a cross-sectional view of a portionof a workpiece 40 that includes a substrate 42 having a primary surface43. The substrate 42 can include a monocrystalline semiconductor wafer,a semiconductor-on-insulator wafer, a flat panel display (e.g., asilicon layer over a glass plate), or another substrate conventionallyused to form electronic devices. The portion of the substrate 42illustrated in FIG. 6 includes a Group 14 element (e.g., carbon,silicon, germanium, or any combination thereof) that is lightly dopedwith an n-type or p-type dopant. An insulating layer 46 is formed overthe substrate 42, and field isolation regions 44 are formed withinportions of the substrate 42. The insulating layer 46 can include a padlayer and a stopping layer (e.g., a polish-stop layer or an etch-stoplayer) that are sequentially formed over the substrate 42 using athermal growth technique, a deposition technique, or a combinationthereof. Each of the pad layer and the stopping layer can include anoxide, a nitride, an oxynitride, or any combination thereof. In anembodiment, the pad layer has a different composition as compared to thestopping layer. In a particular embodiment, the pad layer includes anoxide, and the stopping layer includes a nitride. The field isolationregions 44 can be formed using a shallow trench isolation,local-oxidation-of-silicon, or another technique. The field isolationregions 44 define active regions 48, which are portions of the substrate42 that lie between the field isolation regions 44.

FIG. 7 includes the workpiece of FIG. 6 after forming well regions 52,54, 56, and 58. The insulating layer 46 is removed and an implant screenlayer 50 is formed over the active regions. Well regions 52 and 56 havethe same conductivity type, and well regions 54 and 58 have the oppositeconductivity type as compared to well regions 52 and 56. In a particularembodiment, the well regions 52, 56, and 58 at least in part determinethe dopant concentration of body regions of subsequently formedstructures. The well region 54 can be a channel-stop region. Acombination of the field isolation region 44 and well region 54 can helpto electrically isolate the well regions 52 and 56 from each other. In aparticular embodiment, the well regions 52 and 56 are n-well regions,and well regions 54 and 58 are p-well regions. The well regions 52, 54,56, and 58 are lightly doped, and have dopant concentrations higher thanthe substrate 42. The well regions 52 and 56 may have the same dopantconcentration or different dopant concentrations, and the well regions54 and 58 may have the same dopant concentration or different dopantconcentrations.

The well regions 52 and 56 can be formed during the same dopingoperation or different doping operations, and the well regions 54 and 58may be formed during the same doping operation or different dopingoperation. In an embodiment, when a high-energy ion implanter is used,doped ions can be put at a sufficiently high energy so that dopant isimplanted into the substrate 42 under the field isolation region 44 toform the well region 54. In this embodiment, well regions 54 and 58 canbe formed during the same doping operation. In another embodiment (notillustrated), any or all of the well regions 52, 54, 56, and 58 may beformed before the field isolation region 44. In a particular embodiment,a high-energy ion implanter may not be available, and all of the wellregions 52, 54, 56, and 58 may be formed before the field isolationregion 44. In another particular embodiment, the well region 54 may beformed after patterning the insulating layer 46 to define an opening anddoping the substrate 42 to form the well region 54 before forming thefield isolation region 44. The other well regions 52, 56, and 58 may beformed after forming the field isolation regions.

In another embodiment (not illustrated), one or more of the well regionsmay be omitted. For example, if the dopant concentrations of the bodyregions for the subsequently-formed capacitor and tunnel structure(formed well regions 52 and 56) are greater than the dopantconcentrations of the body regions for the subsequently-formed accessand state transistors, the substrate 42 may have a conductivity type anddopant concentration, such that well region 58 may not be required.

After reading this specification, skilled artisans will appreciate thatdopant concentrations and timing of formation of the well regions 52,54, 56, and 58, both relative to one another and with respect to thefield isolation region 44, can be adjusted to a particular application.Further, not all of the well regions 52, 54, 56, and 58 are required.Thus, the well regions 52, 54, 56, and 58, or the absence thereof, canbe tailored for the particular components that will be formed within thewell regions.

FIGS. 8 and 9 include illustrations of a top view and a cross-sectionalview, respectively, after removing the implant screen layer 50 andforming a dielectric layer 70 and a patterned conductive layer 62. FIG.9 includes a cross-sectional view at sectioning line 9-9 in FIG. 8. Theimplant screen layer 50 is removed, and the dielectric layer 70 isformed over the well regions 52, 56, and 58. The dielectric layer 70 caninclude portions that will be a capacitor dielectric layer over wellregion 52, a tunnel dielectric layer over the well region 56, and a gatedielectric layer over the well region 58. The dielectric layer 70 caninclude an oxide, a nitride, an oxynitride, or any combination thereof.In an embodiment, the thickness of the dielectric layer 70 is no greaterthan approximately 20 nm, and in another embodiment, the dielectriclayer 70 is at least approximately 5 nm. In a particular embodiment, thedielectric layer 70 has a thickness in a range of approximately 11 toapproximately 15 nm. The different portions of the dielectric layer canhave the same composition or different composition, and the samethickness or different thicknesses. The dielectric layer 70 can beformed using a thermal growth technique, a deposition technique, or acombination thereof.

A layer of a polycrystalline or amorphous semiconductor material isformed by depositing the polycrystalline or amorphous semiconductormaterial over the substrate 42 and doped to include a p-type heavilydoped portion and an n-type heavily doped portion to make the layerconductive. The polycrystalline or amorphous semiconductor materialincludes one or more Group 14 elements. In one embodiment, the layer hasa thickness no greater than approximately 500 nm, and in anotherembodiment, the layer has a thickness of at least approximately 50 nm.In a particular embodiment, the layer has a thickness in a range ofapproximately 100 nm to approximately 300 nm. The layer is patterned toform a conductive member 62 and a word line 66, as illustrated in FIG.8. The conductive member 62 is the floating gate for the memory cell.Portions 622 and 624 of the conductive member 62 have oppositeconductivity types. In a particular embodiment, the portion 622 has ap-type conductivity, and the portion 624 and the word line 66 have ann-type conductivity. A subsequently-formed metal-containing layer willbe formed over the portions 622 and 624, so that the portions areelectrically connected to each other to form a floating gate electrodefor the memory cell. Referring to FIG. 9, the part of the conductivemember 62 that is disposed over the well region 52 is an upper electrode72 for a capacitor, another part of the conductive member 62 that isdisposed over the well region 56 is an upper electrode 74 for a tunnelstructure, and still another part of the conductive member 62 that isdisposed over the well region 58 is a gate electrode 76 for a statetransistor. The portion of the word line 66 disposed over the wellregion 58 is a gate electrode 78 for an access transistor.

FIG. 10 includes an illustration of a cross-sectional view after formingintermediate doped regions 82, 84, and 86 and insulating spacers 88.Before forming the intermediate doped regions 82, 84, and 86, an oxidelayer (not illustrated) may be formed by thermally oxidizing theconductive member 62 and word line 66, including upper electrodes 72 and74 and gate electrodes 76 and 78. The oxide layer has a thickness nogreater than approximately 20 nm. In an embodiment, the intermediatedoped regions 82 and 84 have the same conductivity type, and theintermediate doped regions 86 have the opposite conductivity type. In aparticular embodiment, intermediate doped regions 82 and 84 have ap-type conductivity, and the intermediate doped regions 86 have ann-type conductivity. In an embodiment, a patterned masking layer (notillustrated) is formed that includes a masking member (not illustrated)over the well region 58 and an opening over the well regions 52, 54, and56, and the intermediate doped regions 82 and 84 are formed. Thepatterned masking layer is removed, a patterned masking layer (notillustrated) is formed that includes a masking member (not illustrated)over the well region 58 and an opening over the well regions 52, 54, and56, and the intermediate doped regions 82 and 84 are formed. Thepatterned masking layer can be removed, and another masking layer (notillustrated) is formed that includes another masking member (notillustrated) over the well regions 52, 54, and 56, and an opening overthe well region 58, and the intermediate doped regions 86 are formed. Ina particular embodiment, the intermediate doped regions 82, 48, and 86are formed by ion implantation. The intermediate doped regions 82, 84,and 86 can have dopant concentrations of less than 1×10¹⁹ atoms/cm³, andin an embodiment, the intermediate doped regions 82, 84, and 86 havedopant concentrations greater than well regions 52, 56, and 58,respectively. In a particular embodiment, the intermediate doped regions82, 84, and 86 have dopant concentrations in a range of approximately1×10¹⁷ atoms/cm³ to approximately 1×10¹⁸ atoms/cm³. In needed ordesired, the order of forming the patterned masking layers and theintermediate doped regions 82, 84, and 86 can be reversed.

An insulating layer is conformally deposited and anisotropically etchedto form the insulating spacers 88. The insulating spacers 88 include anoxide, a nitride, an oxynitride, or any combination thereof. The widthsof the insulating spacers 88, as measured at their bases, generallycorrespond to the thickness of the insulating layer that is deposited.In an embodiment, the thickness of the insulating layer, as deposited,is no greater than approximately 500 nm, and in another embodiment, thethickness is at least approximately 20 nm. In a particular embodiment,the thickness is in a range of approximately 50 to 200 nm.

Heavily doped regions 92, 94, 95, 96, 98, and 99 are formed within thewell regions 52, 56, and 58, as illustrated and described with respectto FIGS. 11 and 12. In an embodiment, heavily doped regions 92, 96, and98 have a conductivity type opposite that of heavily doped regions 94,95, and 99. In a particular embodiment, heavily doped regions 92, 96 and98 have an n-type conductivity, and heavily doped regions 94, 95, and 99have a p-type conductivity. The heavily doped regions 92, 94, 96, 98,and 99 can have the same dopant concentration or different dopantconcentrations. In a particular embodiment, the heavily doped regions92, 94, 95, 96, 98, and 99 have a dopant concentration of at leastapproximately 1×10²⁰ atoms/cm³. The depths of the heavily doped regions92, 94, 95, 96, 98, and 99 are relatively shallow and may have depths nogreater than approximately 500 nm. In a particular embodiment, thedepths of the heavily doped regions 92, 94, 95, 96, 98, and 99 are in arange of approximately 50 to 300 nm. In the embodiment as illustrated,the heavily doped regions 92 and 95 have junction depths that are deeperthan the intermediate doped regions 82 and 84, respectively.

A patterned masking layer is formed over the workpiece and includesmasking member 114 as illustrated in FIG. 11. A masking member 114closest to the left-hand side of FIG. 11 covers a portion of the wellregion 52 where a well contact region to the well region 52 will beformed, the masking member that covers portions of the well regions 54and 56 where a well contact region to the well region 56 will be formed,and the other masking member covers a remainder of the tunnel structureand covers the state and access transistors. Heavily doped regions 94,95, and 99 are formed through openings in the patterned masking layer.The heavily doped regions 94 and 95 allow electrical contact to be madeto the intermediate doped regions 82 and 84, respectively. In FIG. 11,the right-hand edge of the heavily doped region 95 can be moved so thatit is aligned to the sidewall spacer 88 beside the upper electrode 74 ifneeded or desired. By having the right-hand edge of the heavily dopedregion 95 offset from the sidewall spacer 88, as illustrated in FIG. 11,a higher voltage can be used for erasing without increasing thelikelihood that dielectric layer 70 will break down during erasing. Theheavily doped region 99 is a well contact region for the well region 58.If the well region 58 would not be present, the heavily doped region 99would be a substrate contact region for substrate 42. The patternedmasking layer that includes masking members 114 is removed.

Another patterned masking layer is formed over the workpiece andincludes masking member 126 as illustrated in FIG. 12. A masking member126 closest to the left-hand side of FIG. 12 covers most of thecapacitor except a portion of the well region 52 where a well contactregion to the well region 52 will be formed, the masking member 126 nearthe center of FIG. 12 covers most of the tunnel structure except aportion of the well region 56 where a well contact region to the wellregion 56 will be formed, and the other masking member 126 covers thewell contact regions for the well region 58. Heavily toped regions 92,96, and 98 are formed through openings in the patterned masking layer.The heavily doped regions 92 and 96 are well contact regions for thewell regions 52 and 56, respectively. The heavily doped regions 98 aresource, source/drain, and drain regions for the state and accesstransistors. The patterned masking layer that includes masking members126 is removed. In needed or desired, the order of forming the patternedmasking layers and the heavily doped regions 92, 94, 95, 96, 98, and 99can be reversed.

FIG. 13 includes an illustration after forming a silicide blocking mask134 and depositing a metal layer 132. The silicide blocking mask 134 isa sacrificial layer that will be removed after forming silicide regions.In an embodiment, the silicide blocking layer 134 can include adielectric material, such as a nitride, an oxide, or an oxynitride. Whenthe field isolation regions 44 include oxide and the silicide blockingmask 134 includes an oxide or an oxynitride, the composition of thesilicide blocking mask 134 can be different such that the silicideblocking mask 134 can be etched selectively to the field isolationregions 44. For example, the silicide blocking mask 134 can include anundensified deposited film, have a relatively high concentration ofdopant, or a combination thereof. A short etch is performed to removethe dielectric layer 70 from portions of the well regions and gateelectrodes that are not covered by the silicide blocking mask 134. Themetal layer 132 is deposited over the exposed surface of the workpiece.The metal layer 132 can include a transition metal, and in a specificembodiment, can include a refractory metal. As used herein, refractorymetals and refractory metal-containing compounds can withstand hightemperatures (e.g., melting points of such materials can be at least1400° C.) and have a lower bulk resistivity than heavily dopedsemiconductor materials. An exemplary metal for the metal layer 132 caninclude Ti, Ta, W, Pt, Co, Ir, or another suitable material that canreact with the materials within the well regions and gate electrodes.

FIG. 14 includes an illustration of a cross-sectional view after forminga substantially completed memory cell. The workpiece including the metallayer 132 are heated to allow the conductive layer to react withportions of a semiconductor material to form a metal-semiconductormembers 102, 104, and 106 that include a metal-semiconductor compound.The metal layer 132 does not significantly react with the silicideblocking mask 134 and insulating materials, such as the field isolationregion 44 and the insulating spacers 88. Unreacted portions of the metallayer 132 are removed, and then the silicide blocking mask 134.

The metal-semiconductor members 102 include a semiconductor materialwithin the active regions, and the metal-semiconductor members 104 and106 include a semiconductor material within the conductive member 62(see FIG. 6), which includes the upper electrode 72 and gate electrode76, and within the word line 66, which includes the gate electrode 78.The silicide blocking mask 134 substantially prevents themetal-semiconductor member 104 from forming over the portion of theconductive member that overlies the well region 46, wherein such portioncorresponds to the upper electrode of the tunnel structure. Themetal-semiconductor member 104 electrically connects the differentlydoped portions 622 and 624 of the conductive member 62 to each other.

The memory cell includes a capacitor 122, a tunnel structure 124, astate transistor 126, and an access transistor 128. In the embodiment asillustrated, the capacitor 122 is a PMOS capacitor, and the state andaccess transistors 126 and 128 are n-channel transistors.

Further processing is performed so that the heavily doped regions 92 and94 are coupled to a control gate terminal 1102, the heavily dopedregions 95 and 96 are coupled to an erase terminal 1104, the heavilydoped region 98 closest to the center of FIG. 14 is coupled to a sourceterminal 1106, gate electrode 78 is coupled to an access terminal 1108,the heavily doped region 98 closest to the right-hand side of FIG. 14 iscoupled to a drain terminal 1110, and the heavily doped region 99 iscoupled to a ground or V_(SS) terminal 1112. In a particular embodiment(not illustrated), one or more interlevel dielectric and interconnectlevels are formed to complete formation of the integrated circuit. Inthis embodiment, the heavily doped regions 92 and 94 are coupled to acontrol line, the heavily doped regions 95 and 96 are coupled to anerase line, the heavily doped region 98 closest to the center of FIG. 14is coupled to a source line, gate electrode 78 is coupled to an accessline, the heavily doped region 98 closest to the right-hand side of FIG.14 is coupled to a bit line, and the heavily doped region 99 is coupledto ground or V_(SS) for the integrated circuit. In a more particularembodiment, couplings can be replaced by electrical connections. Forexample, the heavily doped regions 92 and 94 are electrically connectedto a control gate terminal 1102 the heavily doped region 95 and 96 areelectrically connected to an erase terminal 1104, the heavily dopedregion 98 closest to the center of FIG. 14 is electrically connected toa source terminal 1106, gate electrode 78 is electrically connected toan access terminal 1108, the heavily doped region 98 closest to theright-hand side of FIG. 14 is electrically connected to a drain terminal1110, and the heavily doped region 99 is electrically connected to aground or V_(SS) terminal 1112.

In an embodiment (not illustrated), one or more interlevel dielectricand interconnect levels are formed to complete formation of theintegrated circuit. In this embodiment, the heavily doped regions 92 and94 are coupled to a control line, the heavily doped regions 95 and 96are coupled to an erase line, the heavily doped region 98 closest to thecenter of FIG. 14 is coupled to a source line, gate electrode 78 iscoupled to an access line, the heavily doped region 98 closest to theright-hand side of FIG. 14 is coupled to a bit line, and the heavilydoped region 99 is coupled to ground or V_(SS) for the integratedcircuit.

Although not illustrated, other electrical components are formed usingthe process flow as previously described. For example, electroniccomponents within program, erase, and read units, and if present, withinthe logic block can be formed using the process flow described above.Because the NVM cells are formed using a single poly process, ratherthan a double poly process, the NVM cells can be formed without addingany additional operations used to form electronic components, andparticularly transistor structures, outside of the NVM cell array.

The operations of the memory cell are discussed with respect to thememory cell 3100 in FIG. 4 and the physical design in FIG. 14. During aprogram pulse, SL 1370, source terminal 1106, AL 3150, access terminal1108, BL 3160, and drain terminal 1110 are at approximately 0 volts orV_(SS). CL 3140, control gate terminal 1102, EL 3130, and erase terminal1104 are at approximately V_(PP). In a particular embodiment, V_(PP) isin a range of approximately 10 volts to approximately 18 volts. Duringthe erase pulse, electrons within the well region 58 tunnel into thegate electrode 76 of the state transistor 126. Thus, charge carrierspass through the dielectric layer 70 (that is, the gate dielectriclayer) of the state transistor 126. The charge carriers affect thevoltage of the floating gate for the memory cell. When the chargecarriers are electrons, the voltage of the floating gate is reducedduring a program pulse.

During an erase pulse, CL 3140, control gate terminal 1102, SL 1370,source terminal 1106, AL 3150, access terminal 1108, BL 3160, and drainterminal 1110 are at approximately 0 volts or V_(SS). EL 3130 and eraseterminal 1104 are at approximately V_(PP). During the erase pulse,electrons within the floating gate tunnel into the well region 56 of thetunnel structure 124. Thus, charge carriers pass the through thedielectric layer 70 of the tunnel structure 124. The charge carriersaffect the voltage of the floating gate for the memory cell. When thecharge carriers are electrons, the voltage of the floating gate isincreased during an erase pulse.

Thus, with the memory cell in accordance with the embodiment asillustrated in FIG. 14, charge carriers pass through the dielectriclayer 70 of the state transistor 126 during a program pulse, and chargecarriers pass through the dielectric layer 70 of the tunnel structure124 during an erase pulse. Compare the memory cell as illustrated inFIG. 1, wherein charge carriers pass through the dielectric layer of thecapacitor 14 both during a program pulse and during an erase pulse.Accordingly, for the same number of program and erase cycles, morecharge can be trapped within the dielectric of the capacitor 14 ascompared to each of the dielectric layer 70 of the state transistor 126and the dielectric layer 70 of the tunnel structure 124. Therefore, thememory cells in FIGS. 4 and 12 are more resistant to dielectricbreakdown during normal operation of the memory cells, as compared tothe memory cells of FIG. 1.

During a reading operation, SL 1370 and source terminal 1106 are atapproximately 0 volts or V_(SS). CL 3140, control gate terminal 1102, EL3130, and erase terminal 1104 are at approximately V_(Gread). In anembodiment, V_(Gread) is approximately V_(DD). AL 3150 and accessterminal 1108 are at approximately V_(Access), which is approximatelyV_(DD). The voltage for V_(DD) will vary depending on the technologyused. V_(DD) can be in a range of approximately 0.9 volts toapproximately 5.0 volts. BL 3160 and drain terminal 1110 may bepre-charged to a predetermined voltage, such as V_(DD), ½ V_(DD), oranother voltage other than the voltage on SL 1370 and the sourceterminal 1106, before the read operation begins. During the readoperation, a sense amplifier and other circuitry within the read unitcan be coupled to BL 3160 and can determine the state of the memory cell3100. If the voltage on BL 3160 remains above a predetermined threshold,no significant current flows through the state transistor 126, and thememory cell is determined to be in a program state. If the voltage on BL3160 is reduced below the predetermined threshold, significant currentflows through the state and access transistors 126 and 128, and thememory cell is determined to be in an erased state.

The tunnel structure 124 has significant features. The intermediatedoped region 84 may or may not abut the metal-semiconductor member 102overlying the heavily doped region 96. Further, the intermediate dopedregion 84 is significantly more heavily doped as compared to the wellregion 56. In a particular embodiment, the intermediate doped region 84has a p-type conductivity, and the well region 56 and heavily dopedregion 96 have an n-type conductivity. The intermediate doped region 84can form a leaky junction with the metal-semiconductor member 102, theheavily doped region 96, or both. During an erase pulse and a programpulse, the voltage on the erase terminal 1104 can be sufficiently highenough to cause breakdown between the intermediate doped region 84 andeither or both of the metal-semiconductor member 102 and heavily dopedregion 96. Thus, during an erase or program pulse, the voltage on theintermediate doped region 84 can approach the voltage on the eraseterminal 1104. The intermediate doped region 84 can help to control thespace charge region that forms within the well region 56 to be limitedto the portion of the well region 56 that directly underlies the upperelectrode 74. Thus, the tunnel structure 124 may not go into deepdepletion during an erase pulse.

Another tunnel structure can be used for the tunnel structure 124. FIG.15 includes a top view of a partially-formed tunnel structure 154. Thefield isolation region 44, well region 56, and the conductive memberincluding the upper electrode 74 are formed using any of the embodimentsas previously described. A mask is formed and has a shape as illustratedby dashed line 1584. The mask covers the field isolation region 44 andportions of the well region 56 immediately adjacent to the fieldisolation region 44. The mask defines an opening in which the upperelectrode 74 and portions of the well region 56 immediately adjacent tothe upper electrode 74 are exposed. A doping operation forms anintermediate doped region substantially similar to the intermediatedoped region 84 except that the intermediate doped region using the maskwould not extend to the field isolation region 44. For example, thefirst intermediate doped region can have an edge that is disposedbetween and spaced apart from the second electrode and an outer edge ofthe active region, wherein the outer edge is define by the fieldisolation region. The mask is removed, and although not illustrated, aninsulating spacer 88 and a heavily doped region within the well region56 are formed. The heavily doped region would be substantially similarto the heavily doped region 96. Unlike the heavily doped region 96, theheavily doped region formed using the embodiment as illustrated in FIG.15 can have a junction depth that is shallower than the intermediatedoped region and still make good contact with the well region 56.

The different tunnel structures as described herein can have differenterase voltages. The description of voltages for erasing are presentedsolely to allow for a comparisons of erase voltages between differenttunnel structures and not to limit any tunnel structure to a specificset of erasing voltages. For a memory cell being erased, the controlterminal, source terminal, word line, and drain terminal are all at 0volts. During an erase pulse, the tunnel structures 124 and 154 can beerased when the erase terminal is in a range of approximately 9.1 voltsto approximately 9.6 volts. Although higher voltages than thosedescribed can be used, a lower voltage can allow a smaller charge pumpwithin the erase unit to be used.

Other embodiments can be used without deviating from the scope of thepresent invention. The orientation of the memory array 31 can be changedby reversing rows and columns. In a particular embodiment, theillustration in FIG. 4 can be rotated 90°. The erase lines remainparallel to the control lines. In another embodiment, referring to FIG.14, the portions of the heavily doped regions 94 and 96 do not need tobe disposed at both sides of the active regions for the capacitor 122and the tunnel structure 124. For example, the portions of the heavilydoped regions 94 and 96 that are not disposed under a terminal (that is,the control gate terminal 1102 or the erase terminal 1104) are notrequired, as other portions of the heavily doped regions 94 and 96underlie the control gate terminal 1102 or the erase terminal 1104 andprovide a good ohmic contact to the corresponding well regions.

Further, the metal-semiconductor members 102, 104, and 106 can be formedat different times or may be replaced by another material. Referring toFIG. 8, after forming and doping the conductive layer for the conductivemembers 62 and 66, a metal-containing layer can be formed over theconductive layer before patterning to form conductive members 62 and 66.The metal-containing layer can include any of the materials aspreviously described with respect to the metal-semiconductor members102, 104, and 106. Additionally, the metal-containing layer can includea metal-nitride or metal-semiconductor-nitride compound. Themetal-nitride or metal-semiconductor-nitride compound many be conductiveand act as an antireflective layer. Still further, a reaction may or maynot be performed. The metal-containing layer can be in elemental form ormay be deposited as a compound. With respect to the metal-semiconductormembers 102, a contact silicidation process can be performed rather thanforming the metal-semiconductor members 102 as illustrated.

A more robust NVM cell can be formed that is more resistant todielectric breakdown from repeated program and erase cycles of a NVMcell. Further, the architecture of the NVM array 31 and its operationreduces the likelihood of an erase disturb of unselected memory cellswhen erasing selected memory cells. Thus, data integrity is better forthe NVM array 31 as compared to the NVM array 10 of FIG. 1. Stillfurther, the process flow for forming the NVM array 31 can besubstantially the same as a process flow for forming transistors withinlogic block of the integrated circuit.

The memory cells as described herein allow the intermediate dopedregions 84 to be biased using the erase terminal 1104, via themetal-semiconductor member 102 and the heavily doped region 95. Althoughnot prior art under US patent law, each of US 2011/0316060, US2011/0316067, and US 2011/0317492 discloses nonvolatile memory cells(“other memory cells”), wherein intermediate doped regions 84 canelectrically float. The memory cells as disclosed herein can providefurther benefits beyond the other memory cells. As will be describedlater in this specification, the memory cells as described herein can beprogrammed and erased at lower voltages and allow the memory cells towithstand more program-erase cycles as compared to the other memorycells and other convention memory cells formed using a singlepolysilicon logic process flow, such as disclosed in US 2006/0220096(“conventional memory cells”). In an embodiment, at 100,000program-erase cycles at 135° C., the failure rate of conventional memorycells or other memory cells can be at least approximately one,approximately two, or approximately three orders of magnitude higherthan the memory cells as described herein. In another embodiment, at afailure rate of 10 ppm, the memory cells as described herein canwithstand at least approximately two, approximately five, orapproximately nine times the number of program-erase cycles at 135° C.as compared to the conventional memory cells or the other memory cells.

After reading this specification, skilled artisans will appreciate thatmany different layouts and processing operations can be used withoutdeviating from the present invention. The layout as illustrated in FIG.8 is provided to simplify understanding of an exemplary layout for amemory cell. Many other layouts can be used, and a more compact cell canbe formed in another embodiment. The exact physical orientation of eachcomponent within the memory cell can be changed as long as the couplingsand electrical connections described herein are maintained. The order ofsome processing operations can be changed if needed or desired.

The memory cell in the embodiment as illustrated and described in FIG.14 is programmed and erased using Fowler-Nordheim tunneling. In anotherembodiment, the memory cell of FIG. 14 may be programmed using hotcarrier injection. In this embodiment, the voltage on CL 3140, controlgate terminal 1102, EL 3130, and erase terminal 1104 can be in a rangeof approximately 6 volts to approximately 8 volts, SL 3170 and sourceterminal 1106 are at approximately 0 volts or V_(SS), and AL 3150,access terminal 1108, BL 3160, and drain terminal 1110 can be in a rangeof approximately 4 to approximately 6 volts. In this particularembodiment, electrons can be injected into the floating gate at the gateelectrode 76 of the state transistor 126. All unselected lines andterminals would be at substantially 0 volts, and therefore, the NVMarray 31 may be more resistant to program disturb issues as compared tothe NVM array 10 in FIG. 1. If program performance for hot carrierinjection is to be improved, a p-type halo region could be formed nearthe drain of the state transistor 126. The erase operation can remainthe same, and thus, carriers pass through dielectric layers of differentcomponents during program and erase pulses.

In yet further embodiments, the program and erase states can bereversed, such that the program state corresponds to a relatively higherfloating gate voltage, and the erase state corresponds to a relativelylower floating gate voltage. Such an embodiment can be achieved byreversing the polarities of the voltages in the erase and programportions of the table in FIG. 5. For example, Vpp can be approximately−10 volts to approximately −18 volts. In addition, conductivity typesmay be reversed.

After reading this specification, skilled artisans will appreciate theflexibility in implementing different layouts, processing flows,operating techniques (program, erase, read), or any combination thereofthat allow the NVM memory cell array to be tailored to a particularapplication. Thus, the NVM memory cell array can be integrated into anexisting logic process flow, using existing program, erase, and readunits for NVM memories with no or only some changes.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention.

In a first aspect, an electronic device including a tunnel structure caninclude a substrate having a primary surface and an active region, afirst electrode including a lightly doped region of the substrate,wherein the first electrode extends to the primary surface and has afirst conductivity type, and a second electrode disposed over the firstelectrode, wherein at least a portion of the second electrode has thefirst conductivity type. The tunnel structure can further include atunnel dielectric layer disposed between the first and secondelectrodes, and a first intermediate doped region of the substrate,wherein the first intermediate doped region abuts the lightly dopedregion, has a second conductivity type opposite the first conductivitytype, and has a dopant concentration that is greater than a dopantconcentration of the lightly doped region. The tunnel structure canstill further include a first heavily doped region of the substrate,wherein the first heavily doped region contacts the first intermediatedoped region, has the second conductivity type and a dopantconcentration that is higher than the dopant concentration of the firstintermediate doped region. The tunnel structure can also include asecond heavily doped region of the substrate, wherein the second heavilydoped region contacts the lightly doped region, has the firstconductivity type and a dopant concentration that is higher than thedopant concentration of the first intermediate doped region, and iselectrically connected to the first heavily doped region.

In an embodiment of the first aspect, the electronic device furtherincludes a strapping member that electrically connects the first andsecond heavily doped regions together. In a particular embodiment, thestrapping member includes a transition metal silicide. In anotherparticular embodiment, the strapping member does not overlie the firstintermediate doped region. In another embodiment, the electronic devicefurther includes a sidewall spacer adjacent to the second electrode,wherein the sidewall spacer overlies the first intermediate doped regionbut does not overlie the first or second heavily doped region. In stillanother embodiment, the dopant concentration of the first heavily dopedregion is at least one order of magnitude higher than the dopantconcentration of the first intermediate doped region.

In a further embodiment of the first aspect, the electronic devicefurther includes a second intermediate doped region spaced apart fromthe first intermediate doped region, wherein the second electrode has afirst side and a second side, the first intermediate doped region isdisposed closer to the first side than the second side, and the secondintermediate doped region is disposed closer to the second side than thefirst side. In a particular embodiment, substantially all of the secondelectrode has the first conductivity type over the active region, thefirst and second intermediate doped regions have substantially a samedopant concentration, and each of the first and second heavily dopedregions is disposed closer to the first side of the second electrodethan the second side of the second electrode. From a top view, the firstheavily doped region is disposed between the first intermediate dopedregion and the second heavily doped region. In another particularembodiment, a first portion of the second electrode has the secondconductivity type at the first side of the second electrode, and asecond portion of the second electrode has the first conductivity typeat the second side. In a more particular embodiment, the electronicdevice further includes a second intermediate doped region spaced apartfrom the first intermediate doped region, wherein the first intermediatedoped region is disposed closer to the first portion of the secondelectrode than the second portion of the second electrode, and thesecond intermediate doped region has the first conductivity type and isdisposed closer to the second portion of the second electrode than thefirst portion of the second electrode.

In a second aspect, a process of forming an electronic device caninclude providing a substrate including a lightly doped region at aprimary surface, wherein the lightly doped region has a firstconductivity type, forming a tunnel dielectric layer over the firstelectrode, and forming a second electrode of the tunnel structure overtunnel dielectric layer, wherein at least a part of the second electrodehas the first conductivity type. The process can also include forming afirst intermediate doped region within a portion of the lightly dopedregion, wherein the first intermediate doped region is at the primarysurface, abuts the lightly doped region, has a second conductivity typeopposite the first conductivity type, and has a dopant concentrationthat is greater than a dopant concentration of the lightly doped region.The process can further include forming a first heavily doped region atthe primary surface, wherein the first heavily doped region abuts thefirst intermediate doped region and has the second conductivity type anda concentration that is higher than the first intermediate doped region,and forming a second heavily doped region at the primary surface,wherein the first heavily doped region is at the primary surface,contacts the lightly doped region, has the first conductivity type and aconcentration that is higher than the first intermediate doped region.From a top view, the first heavily doped region can be disposed betweenthe first intermediate doped region and the second heavily doped region.

In an embodiment of the second aspect, the process further includesforming a strapping member that electrically connects the first andsecond heavily doped regions together. In a particular embodiment, thestrapping member includes a transition metal silicide. In anotherparticular embodiment, the strapping member does not overlie the firstintermediate doped region. In another embodiment, the process furtherincludes forming a sidewall spacer adjacent to the second electrode,wherein the sidewall spacer overlies the first intermediate doped regionbut does not overlie the first or second heavily doped region. In aparticular embodiment, the process further includes forming a mask afterforming the second electrode and the first intermediate doped region,wherein the mask defines an opening over the second electrode and only apart of the first intermediate region, and forming the first heavilydoped region including implanting a dopant through the opening in themask and into the lightly doped region. In a more particular embodiment,the mask includes a mask feature that covers the second electrode andthe sidewall spacer.

In a further embodiment of the second aspect, forming the firstintermediate region includes doping a portion of the lightly dopedregion to a dopant concentration no greater than approximately 1×10¹⁸atoms/cm³. In still a further embodiment, the process further includesforming a second intermediate doped region spaced apart from the firstintermediate doped region, wherein the second electrode has a first sideand a second side, the first intermediate doped region is disposedcloser to the first side than the second side, and the secondintermediate doped region is disposed closer to the second side than thefirst side. In a particular embodiment, forming the second electrode isperformed such that substantially all of the second electrode over thefirst electrode has the first conductivity type.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Example

The concepts described herein will be further described in the Example,which do not limit the scope of the invention described in the claims.The Example demonstrates that memory cells as described herein have anacceptable threshold voltage (V_(Th)) window and can withstand moreprogram-erase cycles compared to the other and conventional memorycells.

A memory array has a circuit as illustrated in FIG. 4 and a memory cellas illustrated in FIG. 14. VPP for programming is 8.8 V, and VPP forerasing is 9.4 V. FIG. 16 illustrates the threshold voltage distributionof the memory cells after programming (line closer to the right-handside of FIG. 16) and after erasing (line closer to the left-hand side ofFIG. 16). The voltage difference between the lowest threshold voltage ofa programmed memory cell and the highest threshold voltage of an erasedmemory cell is the V_(Th) window. For the memory cells, the V_(Th)window is approximately 0.6 V. A V_(Th) window of at least 0.5 V issufficient to differentiate programmed from erased memory cells.

Referring to US 2011/0316060 discloses another memory array has acircuit as illustrated in FIG. 4 and a memory cell as illustrated inFIG. 12. VPP for programming is 8.8 V, and VPP for erasing is 9.4 V.FIG. 17 illustrates the threshold voltage distribution of the memorycells after programming (line closer to the right-hand side of FIG. 17)and after erasing (line closer to the left-hand side of FIG. 17). Forthe memory cells in US 2011/0136060, the V_(Th) window is approximately0.1 V, which is too small to differentiate programmed from erased memorycells. To improve the V_(Th) window, VPP for programming is increased to9.0 V, and VPP for erasing is increased to 9.6 V. FIG. 18 illustratesthe threshold voltage distribution of the memory cells after programming(line closer to the right-hand side of FIG. 18) and after erasing (linecloser to the left-hand side of FIG. 18) at the higher voltages. For thememory cells, the V_(Th) window is approximately 1.3 V, which issufficient to differentiate programmed from erased memory cells.

The memory cells in accordance with embodiments of the present inventioncan have improved endurance. In a particular embodiment, the deepdepletion effect that can occur with particular conventional memorycells can be substantially eliminated. The deep depletion effectivelyshields the gate dielectric layer from VPP preventing erasing, and whenthe shielding effect goes away, the gate dielectric layer experiences anearly instantaneous exposure to VPP causing degradation.

FIG. 19 includes a plot of failure rate as a function of program-erasecycles at 135° C. The conventional cells in FIG. 19 correspond to memorycells in US 2006/0220096. At 100,000 program-erase cycles, theconventional cells have approximately 4200 failures per million memorycells, the other cells have approximately 1500 failures per millionmemory cells, and the memory cells of FIGS. 4 and 14 have approximately3.7 failures per million memory cells. At a failure rate of 10 failuresper million memory cells, the conventional memory cells can withstandapproximately 15,000 program-erase cycles, the other memory cells canwithstand approximately 25,000 program-erase cycles, and the memorycells of FIGS. 4 and 14 can withstand approximately 140,000program-erase cycles. The other memory cells have a significantimprovement over the conventional memory cells, and the memory cells ofFIGS. 4 and 14 are have further improvement over both the conventionaland other memory cells. Thus, the memory cells as described herein canwithstand more program-erase cycles and have a lower failure rate fromprogram-erase cycling.

Certain features that are, for clarity, described herein in the contextof separate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges includes each and every value within that range.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. An electronic device comprising: a tunnelstructure comprising: a substrate having a primary surface and an activeregion; a first electrode including a lightly doped region of thesubstrate, wherein the first electrode extends to the primary surfaceand has a first conductivity type; a second electrode disposed over thefirst electrode, wherein at least a portion of the second electrode hasthe first conductivity type; a tunnel dielectric layer disposed betweenthe first and second electrodes; a first intermediate doped region ofthe substrate, wherein the first intermediate doped region abuts thelightly doped region, has a second conductivity type opposite the firstconductivity type, and has a dopant concentration that is greater than adopant concentration of the lightly doped region; a first heavily dopedregion of the substrate, wherein the first heavily doped region contactsthe first intermediate doped region, has the second conductivity typeand a dopant concentration that is higher than the dopant concentrationof the first intermediate doped region; and a second heavily dopedregion of the substrate, wherein the second heavily doped regioncontacts the lightly doped region, has the first conductivity type and adopant concentration that is higher than the dopant concentration of thefirst intermediate doped region, and is electrically connected to thefirst heavily doped region.
 2. The electronic device of claim 1, furthercomprising a strapping member that electrically connects the first andsecond heavily doped regions together.
 3. The electronic device of claim2, wherein the strapping member comprises a transition metal silicide.4. The electronic device of claim 2, wherein the strapping member doesnot overlie the first intermediate doped region.
 5. The electronicdevice of claim 1, further comprising a sidewall spacer adjacent to thesecond electrode, wherein the sidewall spacer overlies the firstintermediate doped region but does not overlie the first or secondheavily doped region.
 6. The electronic device of claim 1, wherein thedopant concentration of the first heavily doped region is at least oneorder of magnitude higher than the dopant concentration of the firstintermediate doped region.
 7. The electronic device of claim 1, furthercomprising a second intermediate doped region spaced apart from thefirst intermediate doped region, wherein: the second electrode has afirst side and a second side; the first intermediate doped region isdisposed closer to the first side than the second side; and the secondintermediate doped region is disposed closer to the second side than thefirst side.
 8. The electronic device of claim 7, wherein: substantiallyall of the second electrode has the first conductivity type over theactive region; the first and second intermediate doped regions havesubstantially a same dopant concentration; each of the first and secondheavily doped regions is disposed closer to the first side of the secondelectrode than the second side of the second electrode; and from a topview, the first heavily doped region is disposed between the firstintermediate doped region and the second heavily doped region.
 9. Theelectronic device of claim 7, wherein a first portion of the secondelectrode has the second conductivity type at the first side of thesecond electrode, and a second portion of the second electrode has thefirst conductivity type at the second side.
 10. The electronic device ofclaim 9, further comprising a second intermediate doped region spacedapart from the first intermediate doped region, wherein: the firstintermediate doped region is disposed closer to the first portion of thesecond electrode than the second portion of the second electrode; andthe second intermediate doped region has the first conductivity type andis disposed closer to the second portion of the second electrode thanthe first portion of the second electrode.
 11. A process of forming anelectronic device comprising: providing a substrate including a lightlydoped region at a primary surface, wherein the lightly doped region hasa first conductivity type; forming a tunnel dielectric layer over thefirst electrode; forming a second electrode of the tunnel structure overtunnel dielectric layer, wherein at least a part of the second electrodehas the first conductivity type; forming a first intermediate dopedregion within a portion of the lightly doped region, wherein the firstintermediate doped region is at the primary surface, abuts the lightlydoped region, has a second conductivity type opposite the firstconductivity type, and has a dopant concentration that is greater than adopant concentration of the lightly doped region; forming a firstheavily doped region at the primary surface, wherein the first heavilydoped region abuts the first intermediate doped region and has thesecond conductivity type and a concentration that is higher than thefirst intermediate doped region; and forming a second heavily dopedregion at the primary surface, wherein the first heavily doped region isat the primary surface, contacts the lightly doped region, has the firstconductivity type and a concentration that is higher than the firstintermediate doped region, wherein from a top view, the first heavilydoped region is disposed between the first intermediate doped region andthe second heavily doped region.
 12. The process of claim 11, furthercomprising forming a strapping member that electrically connects thefirst and second heavily doped regions together.
 13. The process ofclaim 12, wherein the strapping member comprises a transition metalsilicide.
 14. The process of claim 12, wherein the strapping member doesnot overlie the first intermediate doped region.
 15. The process ofclaim 11, further comprising forming a sidewall spacer adjacent to thesecond electrode, wherein the sidewall spacer overlies the firstintermediate doped region but does not overlie the first or secondheavily doped region.
 16. The process of claim 15, further comprisingforming a mask after forming the second electrode and the firstintermediate doped region, wherein: the mask defines an opening over thesecond electrode and only a part of the first intermediate region; andforming the first heavily doped region comprising implanting a dopantthrough the opening in the mask and into the lightly doped region. 17.The process of claim 16, wherein the mask includes a mask feature thatcovers the second electrode and the sidewall spacer.
 18. The process ofclaim 11, wherein forming the first intermediate region comprises dopinga portion of the lightly doped region to a dopant concentration nogreater than approximately 1×10¹⁸ atoms/cm³.
 19. The process of claim11, further comprising forming a second intermediate doped region spacedapart from the first intermediate doped region, wherein: the secondelectrode has a first side and a second side; the first intermediatedoped region is disposed closer to the first side than the second side;and the second intermediate doped region is disposed closer to thesecond side than the first side.
 20. The process of claim 19, whereinforming the second electrode is performed such that substantially all ofthe second electrode over the first electrode has the first conductivitytype.